The invention relates to new conjugated copolymers of dithienothiophene with vinylene or acetylene (ethinylene). The invention further relates to methods of their preparation, to their use as semiconductors or charge transport materials in optical, electrooptical or electronic devices including field effect transistors, electroluminescent, photovoltaic and sensor devices. The invention further relates to field effect transistors and semiconducting components comprising the new polymers.
Organic materials have recently shown promise as the active layer in organic based thin film transistors and organic field effect transistors [see reference 1]. Such devices have potential applications in smart cards, security tags and the switching element in flat panel displays. Organic materials are envisaged to have substantial cost advantages over their silicon analogues if they can be deposited from solution, as this enables a fast, large-area fabrication route.
The performance of the device is principally based upon the charge carrier mobility of the semiconducting material and the current on/off ratio, so the ideal semiconductor should have a low conductivity in the off state, combined with a high charge carrier mobility ( greater than 1xc3x9710xe2x88x923 cm2Vxe2x88x921 sxe2x88x921). In addition, it is important that the semiconducting material is relatively stable to oxidation, i.e., it has a high ionisation potential, as oxidation leads to reduced device performance.
Compounds known in the prior art which have been shown to be effective p-type semiconductors for organic FETs are dithienothiophene (DTT) (1) and its fused dimer xcex1,xcex1xe2x80x2-bis(dithieno[3,2-b:2xe2x80x2,3xe2x80x2-d]thiophene (BDT) (2) having the structures shown below [see reference 2-4]. 
In particular BDT, which has been extensively studied, has been shown to be an effective p-type semiconductor for organic FETs with a very high charge carrier mobility between 1xc3x9710xe2x88x923 and 5xc3x9710xe2x88x922 cm2Vxe2x88x921 sxe2x88x921 and very high current on/off ratios (up to 108). BDT also has been found in the solid state to have a completely coplanar formation, and to be more planar than oligomers of thiophene.
However, BDT has a high melting point and is very insoluble, therefore, if used as the active layer in an organic thin film transistor, it cannot be readily solution processed. As a result, for applications like FETs, prior art materials like BDT are usually deposited as a thin film by vacuum deposition, which is an expensive processing technique that is unsuitable for the fabrication of large-area films. To improve the solubility of BDT, several substituted derivatives have so far been synthesized (3), [see reference 4] but these have still required vacuum processing when used in thin film transistors.
It is an aim of the present invention to provide new materials for use as semiconductors or charge transport materials, which are easy to synthesize, have high charge mobility and are easily processible to form thin and large-area films for use in semiconductor devices. Other aims of the invention are immediately evident to those skilled in the art from the following description.
The inventors have found that these aims can be achieved by providing new vinylene or acetylene copolymers of dithienothiophene (DTT).
Polymers containing DTT have been previously synthesised. DTT can be polymerised electrochemically but an insoluble material containing many structural defects is produced [see reference 5,6]. Similarly copolymers with dithienopyrrole have also been made (4) [see reference 7]. DTT has also been incorporated into vinylidene polymers either via Knoevenagel (5) [see reference 8] or Wittig reactions (6) [see reference 9]. The latter gave insoluble polymers, whereas the former produced polymers that were soluble but had only moderate photovoltaic or photoconductive behaviour. 
DTT dimers and homo polymers of DTT and copolymers of DTT and thiophenes are reported in the international patent application WO 99/12989 [reference 10]. However, no characterisation or details of the synthetic route of the polymers are disclosed.
The invention relates to new conjugated copolymers comprising at least one dithienothiophene recurring unit and at least one vinylene or acetylene (ethinylene) recurring unit, wherein the dithienothiophene and the vinylene unit may be substituted or unsubstituted.
The invention further relates to the use of polymers according to the invention as semiconductors or charge transport materials, in particular in optical, electrooptical or electronic devices, like for example in field effect transistors (FET) as components of integrated circuitry, as thin film transistors in flat panel display applications or for Radio Frequency Identification (RFID) tags, or in semiconducting components for organic light emitting diode (OLED) applications such as electroluminescent displays or backlights of, e.g., liquid crystal displays, for photovoltaic or sensor devices, as electrode materials in batteries, as photoconductors and for electrophotographic applications like electrophotographic recording.
The invention further relates to a field effect transistor, for example as a component of integrated circuitry, as a thin film transistor in flat panel display applications, or in a Radio Frequency Identification (RFID) tag, comprising one or more poly(dithienothiophene vinylenes) according to the invention.
The invention further relates to a semiconducting component, for example in OLED applications like electroluminescent displays or backlights of, e.g., liquid crystal displays, in photovoltaic or sensor devices, as electrode materials in batteries, as photoconductors and for electrophotographic applications, comprising one or more poly(dithienothiophene vinylenes) according to the invention.
The invention further relates to a security marking or device comprising an RFID or ID tag or a FET according to the invention.